The present aspects generally relate to data storage systems, and more particularly to generating position error signals using readback signal distortion in data storage devices such as disc drives.
Mass storage devices are one of many components of modern computers. One type of mass storage device is a disc drive. In general, disc drives read and write information along concentric tracks formed on discs. A magnetic disc drive, which is a particular type of disc drive, includes one or more magnetic discs mounted for rotation on a hub or spindle. A typical magnetic disc drive also includes a head that flies above each magnetic disc. An actuator moves the head radially over the disc surface for track seek operations and holds the head directly over a track on the disc surface for track following operations.
Information is typically stored in concentric tracks on the surface of a magnetic disc by providing a write signal to the head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the actuator so that the head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a readback signal based on those flux reversals. The readback signal is typically conditioned and then decoded by a drive channel and controller to recover data represented by flux reversals stored on the magnetic disc.
A typical disc drive read channel includes the head, signal conditioning circuitry (such as amplification and filtering) and data detection circuits. Error detection and correction is typically performed by the drive controller.
To locate a particular track on a disc, disc drives typically use embedded servo fields on the disc. Thus, a typical disc format comprises “pie-shaped” wedges of servo information interweaved between sections of data. The embedded servo fields are utilized by a servo sub-system to position a head over a particular track. During track following, servo information sensed by the head is demodulated to generate a position error signal (PES) which provides an indication of the radial distance between the head and the track center. The PES is then converted into an actuator control signal, which is used to control the actuator that positions the head.
A fundamental barrier to improved servo performance in disc drives is a servo sampling rate limitation due to format efficiency. The disc/servo format affects both the sampling rate of a digital control system and its sensing noise. When moving to higher track densities, the sampling rate must be increased and the sensing noise diminished. Increasing the sampling rate requires increasing the number of servo sectors on the disc, and decreasing sensing noise requires increasing the size of each servo sector. Together, these effects diminish format efficiency in disc drives.
The present aspects address these problems and offer other advantages over the prior art.